今天看到了一個很有意思的詞spectator ions旁觀離子，以前學化學的時候沒有注意到。就像上圖中的反應方程式，硝酸根和鈉離子反應前後都沒有發生變化，這個就是旁觀離子。
A spectator ion is a charged atom or group of atoms in a chemical reaction that does not undergo a chemical change or change state when the reaction takes place. In chemical reactions, compounds that contain ions are often dissolved in water, resulting in a state called aqueous ions. When two ionic compounds are dissolved into an aqueous state, or both are dissolved into the same solvent, their ions separate, so any ions that made up the first compound can interact with any ions from the second compound. It is not necessary for all ions to interact in this state, and if some ions do not interact, they usually remain dissolved in solution.